摘要:

It appears that prostaglandin E2 (PGE2) stimulates pituitary GH release by acting both on hypothalamic and pituitary sites. To determine if the hypothalamic components are at least in part mediated by an inhibition of somatostatin secretion, several experiments were conducted. In vivo treatment of male rats with indomethacin (Id, 2.5 mg/ 100 g BW, single s.c. injection 24 h before) or in vitro administration of the drug (100 μM) to suppress prostaglandin (PG) synthesis, induced a transient increase in basal in vitro release of somatostatin by median eminence (ME) fragments and did not alter that of medial basal hypothalamic (MBH) fragments. Incubation of ME or MBH fragments from males with different concentrations of PGE2 (0.0028–2.8 μM) or PGF2α (0.028–2.8 μM) did not affect basal somatostatin release. PGE2 (0.0028–0.28 μM) also failed to alter the basal release of somatostatin by ME fragments from ovariectomized or ovariectomized, estrogen, progesterone-treated rats. Nevertheless, PGE2 inhibited the stimulatory effect of dopamine (DA) on somatostatin release by ME of male rats. In vitro suppression of PG synthesis with Id failed to facilitate significantly the stimulatory effect of DA on somatostatin release by either ME or MBH fragments, a facilitatory action that would be expected in view of the inhibitory effect of PGE2 on DA-induced somatostatin release. However, if ME fragments from male rats were incubated with PGE2 (0.28 μM) after the in vitro blockade of PG synthesis with Id, an inhibitory effect of the PG on the basal release of somatostatin became apparent, suggesting that incubation of the ME tissue with Id may have resulted in removal of an inhibitory influence exerted by PGE2 and a possible facilititatory effect on somatostatin release exerted by some other factor. Third ventricular injection of PGE2 to intact, conscious, free-moving male rats significantly elevated plasma GH levels 15 min later. A prior i.v. injection of an antisomatostatin serum elevated basal GH levels and produced a remarkable enhancement of the GH release in response to PGE2 indicating that the increase in GH induced by PGE2 was not dependent upon an inhibition of somatostatin release. It is suggested that the effect that PGE2 exerts on the hypothalamus to evoke GH release is primarily mediated by an enhanced secretion of a GH-releasing factor(s). Although PGE2 may play a role in modulating somatostatin release such a role appears to be of only minor

ISSN:0028-3835    

DOI:10.1159/000123042

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

The kinetics of dopamine (DA) uptake were studied in synaptosomal preparations of the neurointermediate lobe (NIL) of the pituitary gland, a region containing the terminals of the tuberoinfundibular dopaminergic neurons. Lineweaver-Burk plots of the initial velocity of DA uptake versus the concentration of DA yielded a single straight line in the NIL. The Km values in the NIL of the rat and the steer were 2.2 ± 0.5 × 10–6M and 2.0 ± 0.1 × 10–6M, respectively. The uptake was predominantly into dopaminergic terminals since preincubation with desipramine did not affect the Vmax or Km of DA uptake. Oberved uptake was predominantly due to transport across the neuronal membrane and not into storage granules, since reserpine caused only a small decrease in uptake. The concentration of the DA metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in the NIL was 3.6 ng/mg protein. The ratio of DA to DOPAC in the NIL (3.73) was similar to that obtained in the medial basal hypothalamus, another region innervated by the tuberoinfundibular dopaminergic neurons. The kinetics of DA uptake in the nerve terminals of the NIL are similar to those observed in the DA terminals in the median eminence. The affinity of uptake in the terminal fields of the tuberoinfundibular system is considerably lower than in terminals of the mesolimbic and nigrostriatal dopaminergic te

ISSN:0028-3835    

DOI:10.1159/000123043

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

The effects of melatonin on the in vivo pituitary LH response to LH-releasing hormone (LHRH) were examined in neonatal male and female rats, in 35- to 44-day-old male rats, and in 35- to 44-day-old male animals which had been either pinealectomized or maintained in constant light for at least 3 weeks before use. Animals were given saline or melatonin (1–100 μg/rat) followed within 30 sec by saline or LHRH (10–1,000 ng/rat) at separate subcutaneous sites. Blood was collected following decapitation either without prior injection or 15, 30, 45, or 60 min afterwards. Serum LH concentrations were determined by double antibody radioimmunoassay. In neonatal male and female rats, melatonin (1 μg) significantly (p < 0.01) suppressed by approximately 65% serum LH at 15 min after LHRH. Suppression was maintained for at least 60 min, a finding which indicates that melatonin blocks rather than delays the response to LHRH. By contrast, in normal, pinealectomized, and constant light older male rats, melatonin (100 μg) had no detectable effect on either the magnitude or the time course of LH release by LHRH. These data extend our previous in vitro findings by demonstrating that melatonin is a potent inhibitor of the in vivo pituitary response to LHRH in neonatal rats but not in older animals. Neither pinealectomy nor constant light, both of which are assumed to reduce pineal melatonin production, for at least 3 weeks before use restores neonatal pituitary responsiveness to the pineal indole in the older a

ISSN:0028-3835    

DOI:10.1159/000123044

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

A continuous flow perifusion system was used to measure the in vitro release rate, and percent release of endogenous norepinephrine (NE) and dopamine (DA) from rat brain fragments. Catecholamines (CA) were measured simultaneously in effluent fractions and in tissue fragments following perifusion using a modified radioenzymatic assay. Employing this perifusion system allows not only quantification of endogenous release, but also permits study of the dynamics of the release process. To validate the system, NE and DA release were measured in effluent from medial basal hypothalamus (MBH) and caudate nucleus (CN) fragments under various temperature and ionic conditions. K+-stimulated release (60 mM KCl), but not the basal release rate, is temperature and calcium dependent. Marked regional differences are seen in the parameters considered. DA release rate from the CN in male rats was 30 times greater than from the MBH. The percent of DA release was 2.5 times greater and there was a 3 times greater final tissue concentration of DA in the CN than in the MBH. Although the release rate of NE from CN fragments was higher than that of the MBH, it did not reach statistical difference. However, the percent of NE release from the CN was close to 4 times greater than the percent release from the MBH, and final tissue concentrations of NE were 87.9 pg/ mg in the CN compared to 1,240 pg/mg in the MBH (postperifusion values). In a group of female rats, only the percent release of NE from the MBH was significantly different from that of similar tissue from male rats. However, the release rate and percent release of DA from the MBH of female rats were significantly lower than that of male rats. It appears that under this in vitro condition there are marked regional and sex differences in the metabolism of CA between the CN and the MBH fragments of male and female rats. Implications of these findings are briefly discussed.

ISSN:0028-3835    

DOI:10.1159/000123045

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

The pattern of prolactin (PRL) secretion following mating consists of two daily surges, one nocturnal and the other diurnal. Under a photoperiod of 14L: 10D, the most commonly used lighting regime, the nocturnal PRL surge occurs at about 7 h after the onset of the dark phase. The present study investigated the influence of various photo-periods, constant light and dark and suprachiasmatic nucleus lesion (SCN) on the initiation and expression of the nightly PRL surges. Females were divided into five groups and each group was exposed to a different photoperiod. The five experimental photoperiods were: 22L:2D, 19L:5D, 14L: 10D, 8L:16D and 3L:21D. Following at least 8 weeks of exposure to a photoperiod the females were mated. Multiple daily blood samples for PRL determination (RIA) were obtained via chronic intra-atrial cannulae. In females exposed to a decreased period of darkness the nocturnal PRL surge was advanced with respect to the onset of the dark phase. Conversely, an increase in the length of the dark period to over 10 h/day caused a delay in the appearance of the PRL surge. When the timing of the PRL surge is calculated with respect to the midpoint of the dark or light cycle, it occurs at about the same time under all but the most extreme photoperiod (3L:21D). Prior to the experiments using constant dark or constant light the animals were habituated to the lighting conditions for 4 months. In constant darkness the nocturnal PRL surge was synchronized among all animals and peaked in the early morning; its magnitude and duration were greater than under both constant light and alternating light schedules. In constant light, irregular elevations of PRL were seen throughout the day. No elevation of PRL was found in SCN-lesioned animals following cervical stimulation. The present study demonstrates that the nocturnal PRL surges during pregnancy and pseudopregnancy are entrained to photoperiod, can be shifted within limits under various photoperiods and cannot be initiated following lesions in the SCN. On the basis of this and other studies, it is proposed that the nocturnal PRL surge resembles other endogenous circadian rhythms in the rat, but requires the external stimulation of mating for its occurrence.

ISSN:0028-3835    

DOI:10.1159/000123046

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

We measured adrenal weights 3 days after left- or sham-adrenalectomy in male Sprague-Dawley rats at 10 ages between 10 and 155 days. Compared to sham-operated rats, the magnitude of the increase in right adrenal weight ranged between 19 and 32% after unilateral adrenalectomy and was significant at 10, 20, 40, 50, and 60 days (p < 0.01). Comparing left with right adrenals in unilaterally adrenalectomized rats, the right was heavier at all ages (p < 0.01); in animals 40 days and younger, this is due to normal adrenal growth rate (0.3 mg/day) as well as compensatory adrenal growth, while in older animals normal growth rate is slow (0.04 mg/day) and this difference in left and right adrenal weights is due primarily to compensatory growth. We conclude from this study that compensatory adrenal growth occurs 3 days after left adrenalectomy at all ages except 15 and 30 days. Resting levels of plasma ACTH and corticosterone did not differ between left- and sham-adrenalectomized rats at any age. The ACTH response to 1 min exposure to ether vapors was markedly reduced in 7- and 12-day-old rats (p < 0.01). We conclude that compensatory adrenal growth is a consistent response 3 days after unilateral adrenalectomy that depends neither on the age at which surgery is performed nor on the capacity of the rat to secrete markedly elevated levels of ACTH.

ISSN:0028-3835    

DOI:10.1159/000123047

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

The distribution of corticotropin (ACTH) and α-melanotropin (α-MSH) in human brain was investigated by radioimmunoassay using an antiserum which recognized h-ACTH1-39 and α-MSH to an equal degree on a molar basis. Significant amounts of material, which migrated on calibrated Sephadex G-50 columns as synthetic h-ACTH1-39 and synthetic α-MSH, were detected in distinct brain areas. The highest concentrations of ACTH and α-MSH were found in the diencephalon (hypothalamus 4.2 and 12.5 pmol/g wet weight, respectively) and in midbrain (periaqueductal gray 0.5 and 1.7 pmol/g, respectively) and smaller quantities in the rhombencephalon and telencephalon. The ACTH concentration in human pituitary (adenohypophysis) was 104-fold greater than that in the hypothalamus. α-MSH was confined to the midpart and/or stalk region of the pitu

ISSN:0028-3835    

DOI:10.1159/000123048

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

The release of oxytocin from isolated posterior lobe of the hypophysis of untreated rats and rats pretreated with α-methy-p-tyrosine (α-MPT) has been studied. The amount of oxytocin released under resting conditions, in response to ouabain was much higher in those preparations which had been pretreated with α-MPT. Dopamine failed to affect the resting release in tissue taken from control rats but it significantly reduced the secretion of oxytocin in tissue dissected from dopamine-deficient rats. Opioid peptides, β-endorphin or D-Ala2-Pro5-enkephalinamide enhanced the release of oxytocin from isolated neural lobe of the hypophysis dissected from untreated rats, but they failed to enhance significantly the release from posterior lobe of rats which had been pretreated by αMPT, Naloxone prevented the effect of the opioid peptides, and by itself significantly reduced the release of oxytocin. The data suggest that (i) dopamine stored in, and released from, the neural lobe may inhibit the secretion of oxytocin; (ii) the release of oxytocin may be continously controlled by an endogenous opioid peptide: opioid peptides may exert their effect via a disinhibitory phenomenon; they remove the inhibitory effect of dopamine on oxytocin release possibly by inhibiting the release of dopa

ISSN:0028-3835    

DOI:10.1159/000123049

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

The purpose of the present study was to investigate in rats, the effects of sound stimulation upon both the pituitary-adrenal activity (evaluated by the levels of serum corticosterone (B)) and brain dopamine (DA) and noradrenaline (NA). Serum B in rats placed inside the experimental chamber without any sound stimulation was increased and brain DA decreased. For this reason, prior to any sound application, animals were kept in the experimental chamber for 115-120 min, when values had returned to basal levels. The results obtained on the effects of sound frequencies between 500 and 4,000 cps indicated a greater response in the rat pituitary-adrenal system to the lowest frequency (500 cps) we studied. Adrenal cortex hyperactivity occurred in the initial stage of daily repeated 500 cps sound stimulation. During extended periods of daily exposure, the activity of the pituitary-adrenal axis gradually diminished. Changes in the pituitary-adrenal activity, induced by sound stimulation, are closely related to changes in brain NA. The results obtained suggest that at least some of the effects of sound stimulation might be mediated by brain noradrenergic pathways and agree with the hypothesis concerning the existence of a central noradrenergic nervous component which could participate in the control of ACTH secretion.

ISSN:0028-3835    

DOI:10.1159/000123050

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

Plasma levels of PRL, GH, FSH, LH, and TSH were studied at various intervals after electric stimulation of the amygdala, in 5 patients in whom electrodes had been chronically implanted in the course of their evaluation for surgical treatment of uncontrollable, temporal lobe seizures. Electric stimulation, but not sham stimulation, elicited in all cases a significant rise in plasma PRL. Plasma GH rose only in 1 patient and TSH in another. No significant changes in plasma FSH or LH were detected. It is suggested that a fine control mechanism of the hypothalamic hypophyseal final common pathway for the control of PRL secretion, may be mediated either by the ventral amygdalohypothalamic pathway or via the stria terminalis.

ISSN:0028-3835    

DOI:10.1159/000123051

出版商:S. Karger AG    

年代:1980

数据来源: Karger